[aclshow]: Add an option -a to display all ACL counters (sonic-net#83)

The current behavior is to display all ACL counters with value greater than 0.
It is necessary to know the whole ACL table to track if certain rule is there or not.

scripts/aclshow

@@ -11,6 +11,7 @@ optional arguments:
   -v,  --version              show program's version number and exit
   -vv, --verbose              verbose output (progress, etc)
   -c,  --clear                clear ACL counters statistics
+  -a,  --all                  show all ACL counters
   -p PORTS,  --ports PORTS    action by specific port list: Ethernet0,Ethernet12
   -r RULES,  --rules RULES    action by specific rules list: Rule_1,Rule_2
   -t TABLES, --tables TABLES  action by specific tables list: Table_1,Table_2
@@ -212,7 +213,7 @@ class AclStat(object):
 
         return str(self.acl_counters[key][type])
 
-    def display_acl_stat(self):
+    def display_acl_stat(self, display_all):
         """
         print out ACL rules and counters
         """
@@ -225,8 +226,8 @@ class AclStat(object):
         header = ACL_HEADER
         aclstat = []
         for rule_key in self.acl_rules.keys():
-            if self.get_counter_value(rule_key, 'packets') == '0' or \
-                    self.get_counter_value(rule_key, 'packets') == 'N/A':
+            if not display_all and (self.get_counter_value(rule_key, 'packets') == '0' or \
+                    self.get_counter_value(rule_key, 'packets') == 'N/A'):
                 continue
             rule = self.acl_rules[rule_key]
             ports = self.acl_tables[rule_key[0]]['ports']
@@ -304,6 +305,7 @@ def main():
     parser = argparse.ArgumentParser(description='Display SONiC switch Acl Rules and Counters',
                                      version='1.0.0',
                                      formatter_class=argparse.RawTextHelpFormatter)
+    parser.add_argument('-a', '--all', action='store_true', help='Show all ACL counters')
     parser.add_argument('-c', '--clear', action='store_true', help='Clear ACL counters statistics')
     parser.add_argument('-p', '--ports', type=str, help='action by specific port list: Ethernet0,Ethernet12', default=None)
     parser.add_argument('-r', '--rules', type=str, help='action by specific rules list: Rule1_Name,Rule2_Name', default=None)
@@ -322,7 +324,7 @@ def main():
         if args.details:
             acls.display_acl_details()
         else:
-            acls.display_acl_stat()
+            acls.display_acl_stat(args.all)
     except Exception as e:
         print(e.message, file=sys.stderr)
         sys.exit(1)